MdePkg/Test: Add SafeIntLib and BaseLib Base64 unit tests

https://bugzilla.tianocore.org/show_bug.cgi?id=2505

* Add unit tests for SafeIntLib class
* Add unit tests for BaseLib Base64 conversion APIs.
* Add Test/MdePkgHostTest.dsc -to build host based unit
  tests
* Update MdePkg.dsc to build target based tests for
  SafeIntLib and BaseLib
* Update MdePkg.ci.yaml to build and run host based
  tests for SafeIntLib and BaseLib

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Acked-by: Hao A Wu <hao.a.wu@intel.com>
Reviewed-by: Bret Barkelew <Bret.Barkelew@microsoft.com>

MdePkg/Test/MdePkgHostTest.dsc

@@ -0,0 +1,30 @@
+## @file
+# MdePkg DSC file used to build host-based unit tests.
+#
+# Copyright (c) 2019 - 2020, Intel Corporation. All rights reserved.<BR>
+# Copyright (C) Microsoft Corporation.
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  PLATFORM_NAME           = MdePkgHostTest
+  PLATFORM_GUID           = 50652B4C-88CB-4481-96E8-37F2D0034440
+  PLATFORM_VERSION        = 0.1
+  DSC_SPECIFICATION       = 0x00010005
+  OUTPUT_DIRECTORY        = Build/MdePkg/HostTest
+  SUPPORTED_ARCHITECTURES = IA32|X64
+  BUILD_TARGETS           = NOOPT
+  SKUID_IDENTIFIER        = DEFAULT
+
+!include UnitTestFrameworkPkg/UnitTestFrameworkPkgHost.dsc.inc
+
+[LibraryClasses]
+  SafeIntLib|MdePkg/Library/BaseSafeIntLib/BaseSafeIntLib.inf
+
+[Components]
+  #
+  # Build HOST_APPLICATION that tests the SafeIntLib
+  #
+  MdePkg/Test/UnitTest/Library/BaseSafeIntLib/TestBaseSafeIntLibHost.inf
+  MdePkg/Test/UnitTest/Library/BaseLib/BaseLibUnitTestsHost.inf